Several abbreviations that are found in the ensuing text and/or in the drawing Figures are defined as follows:
BB base band
DFE digital front-end
FE front-end
HW hardware
IC integrated circuit
LUT look up table
MRC multiradio controller
RF radio frequency
RX receiver
SIC self-interference cancellation
TX transmitter
In practice any transmitted signal can couple into a receiver through signal path parasitics such as, but not limited to, imperfect isolation between antennas and/or the use of two or more signal branches. Depending on the coupling level the interfering TX signal can desensitize a simultaneously operating receiver, such as in full duplex system or in the case of inter-system operation (e.g., two separate radio transceivers that operate simultaneously within one device), and totally degrade or at least significantly impair the operation of the receiver. This problem is made worse by the current trend towards increased chipset integration levels, where more circuits and circuit sub-systems are integrated into one IC or a few closely adjacent ICs.
One potential technique to alleviate this problem is to use a portion of the transmitted signal in the analog domain, such as at the output of a TX power amplifier, in order to cancel the self-interference component in the received signal. This approach requires summing the distorted RX signal with the portion of the TX signal, which in turn requires coupling the TX signal to the summing function so as to have the proper phase and amplitude. However, since the coupled TX signal manipulation is performed at least partially in analog domain, the accuracy and power consumption are not optimal, and in practice can be difficult to implement.
Reference may be had, for example, to U.S. Pat. No. 6,996,164 B1, Self-Interference Removal Using Converted Compensation in a Relayed Communication System, Blount et al., which describes a receiver section of a relayed communication system. A method is described for removal of self-interference that includes modeling downconversion imperfections in an imperfectly downconverted signal from a receiver downconverter. The receiver downconverter is in the receiver section that receives both an intended signal and a self-generated signal from a local associated transmitter that forms a received relayed composite signal. The method compensates for the downconversion imperfections in the received relayed composite signal to produce a compensated composite signal, and cancels self-generated signal portions from the compensated composite signal to provide an output signal for demodulation. The receiver downconverter model imperfections include at least one of quadrature phase offset, quadrature d.c. imbalance, and quadrature amplitude imbalance.